It has already been long known how to expose semiconductors or substrate plates, especially wafers, on one side, in multiple fashion, with relatively great accuracy, in order to build up several semiconductor layers on over the other, each of which displays a special geometry which must lie in a precise predetermined disposition relative to the surface elements of each of the other layers.
During the course of the intensive development of integrated circuit devices, it is normally required that semiconductors or substrate plates, especially wafers, be exposed on both sides, in repeated cycles. With the present state of the art, this problem still has not been overcome. Moreover, an initial two-side exposure can be carried out only on a semiconductor or substrate plate, i.e., a disk, which is not already provided with some special geometry resulting from previous exposures. Such type of an initial exposure, based upon the state of the art, is carried out such that, beforehand, a top and bottom exposure mask with horizontally running planes are placed in planes parallel to one another and then, after introduction into the space between the two exposure masks, the semiconductor of substrate plate is laid upon the lower exposure mask. Next, using thin rods, the semiconductor or substrate plate is run through a rough parallel and rotational alignment relative to the lowe exposure mask, after which final two-sided exposure takes place through the exposure masks. It is understood that such type of rough calibration of the semiconductor or substrate plate relative to the lower exposure mask is insufficient for obtaining a satisfactory coverage of the geometric structures of the exposure masks with other geometric structures that are already disposed on the semiconductors or substrate plates, i.e., for the purpose of carrying out multiple exposures.
The task for the invention is to obtain a process that makes possible multiple exposure of semiconductors or substrate plates, especially wafers, on both sides, with sufficient congruency of the geometrical structures. This is achieved by initially bringing the two exposure masks into contact, plane parallel fashion, following a prior mutual parallel and rotational alignment. In addition to the fixing of their plane parallel adjustment, the relative distance between the two exposure masks in a direction running perpendicularly to their planes is fixed while retaining the plane parallel adjustment as well as the mutually parallel and rotational alignment. The semiconductors or substrate plates are brought into contact plane parallel fashion with a first of the two exposure masks following prior parallel and rotational alignment of those surfaces which are turned toward this exposure mask, and relative approachment to the second exposure mask is connducted while a pre-established, short distance relative to the semiconductor or substrate plate is attained. The plane parallel adjustment as well as the mutually parallel and rotational alignment is retained.
A particularly favorable and reasonable technique for the execution of the process in accord with the invention can be achieved through means of an apparatus of the type already alluded to hereinabove which is characterized by the fact that an auxiliary rotational compound slide table is provided, in addition to a mask support, for accepting the second exposure mask. The drive slide of the first compound slide table, preferably the first rotational compound slide table associated to the first exposure mask, is coupled with the drive slide of the other compound slide table, preferably that associated with the auxiliary rotational compound slide table for the second exposure mask. The mask support frame of the one rotational compound slide table, preferably that of the rotational compound slide table driving the other rotational compound slide table, is connected to its associated rotational compound slide table through a support frame approachment guide running perpendicular to the plane of travel of the two compound slide tables. The mask support frame is constructed as an adjustable wedge-error calibration frame in one of the two compound slide tables, with the wedge-error correction head intended for accepting the semiconductor or substrate plate being bearingly mounted to a swivel arm which, when the mask supports are moved apart, is pivotable in a rotational plane that lies parallel to as well as between the planes of displacement of the two rotational compound slide tables, in the space between the two planes of displacement. The mask support frame is movable into the pivot position perpendicularly to the planes of displacement, opposite the mask support that it turned toward the semiconductors or substrate plates, until the semiconductor or substrate plate comes into contact with the exposure mask associated with this mask support and, which is again pivotable after bringing the semiconductor or substrate plate to the exposure mask turned toward them. Also, at least on the wedge-error correction head, there is provided a controllable support for freeing the semiconductor or substrate plate upon coming into contact with the exposure mask turned toward them (semiconductor or substrate plate), as well as for picking them up after completed exposure.
With an extensively modified apparatus, representing a kinematic reversal of this preferred apparatus, both mask supports are rigidly connected to their associated rotational compound slide tables and the drive slides of the one rotational compound slide table are connected with the drive slides of the other rotational compound slide table through a table approachment guide which runs perpendicular to the planes of displacement of both rotational compound slide tables. The table approachment guide of this modified example of embodiment corresponds, here, to the support approachment guide in the case of the preferred example of embodiment.
By means of the previously described apparatus in accordance with the present invention, and, indeed, as well as for both the preferred and the modified examples of embodiments, it is possible to adjust both exposure masks in planes parallel to one another, first to an acceptable parallel and rotational alignment, which is done with both rotational compound slide tables, through means of the wedge-error calibration frame associated with the one exposure mask and then, while maintaining this adjustment, move the two exposure masks apart through means of the support approachment arrangement, in the case of the preferred example of embodiment, or the table approachment arrangement, so that sufficient space is formed between the two exposure masks to permit introduction of the semiconductor or substrate plate which will be held in place by the wedge-error correction head arranged on the pivoting arm. Through means of the wedge-error correction head that has been pivoted into the space between the two exposure masks, it is now possible to bring the semiconductor or substrate plate into plane parallel contact with one of the two exposure masks, preferably the lower exposure mask, by lowering the wedge-error correction head, whereby any cushion of entrapped air between the semiconductor or substrate plate and the oppositely lying exposure mask can escape. After making the plane parallel adjustment of the semiconductor or substrate plate relative to the exposure mask turned toward it and, along with this, relative to the two exposure masks in the wedge-error correction head, this latter can raise up the semiconductor or substrate plate a short interval from the exposure mask toward which it is turned, whereupon it is now possible, through means of one of the two rotational compound slide tables whose drive slots are engaged in the drive slots of the other rotational compound slide table, to subject both exposure masks together to a parallel and rotational alignment relative to that of the semiconductor or substrate plate that is adjusted along a plane parallel to the two exposure masks. Finally, the esemiconductor or substrate plate can be brought to the exposure mask turned toward it; and in the case of a vertical arrangement one over the other, both exposure masks, by laying the semiconductor or substrate plate on the lower exposure mask. The wedge-error correction head is then outwardly pivotable out of the space between the two exposure masks by means of the pivoting arm, whereupon the exposure mask furthest away from the semiconductor or substrate plate can be lowered to the extent that a two-sided exposure of the semiconductor or substrate plate, lying in axactly parallel and rotational alignment to both exposure masks, can be carried out from either side. A particular advantage of the apparatus in accordance with the invention lies in the fact that, using a single microscope, it is possible to calibrate both exposure masks relative to one another as well as to the geometry of one side of the semiconductor plate relative to the microscopically observed exposure mask, by observation perpendicular to the planes of one of the two exposure masks, whereupon correct calibration of the other side of the semiconductor or substrate plate relative to the other exposure mask is automatically ensured. By exact plane parallel adjustment of the two exposure masks relative to each other as well as of the semiconductor or substrate plate relative to the two exposure masks, the surfaces to be observed through the microscope can be brought very closely together, dependent only upon the depth sharpness range of the microscope used.